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Italian veteran Flavia Pennetta reached the US Open semi-finals for the second time in three years, outsmarting fifth-seed Petra Kvitova 4-6 6-4 6-2 to add to the Czech's Flushing Meadows frustration.

The Italian flag will feature prominently in the semi-finals with the 33-year-old Pennetta joined in the last-four by 32-year-old compatriot Roberta Vinci, who booked her spot on Tuesday with a victory over Frenchwoman Kristina Mladenovic.

Pennetta has always been at home on the New York hardcourts having now advanced to quarter-finals or beyond in six of her last seven visits to the National Tennis Center.

The same courts, however, have not been kind to Kvitova, the two-time Wimbledon champion, who never ventured past the fourth round until this year.

Kvitova, one only two players to beat Serena Williams this season, had been in superb form winning her final US Open tuneup in New Haven and carried that momentum into Flushing Meadows, reaching the quarter-finals without dropping a set.

The joy on Halep's face was obvious as she moved closer to her maiden grand slam title [AP]

Later, second seed Simona Halep, cheered on by Romanian gymnastics great Nadia Comaneci, fought off a determined challenge from former world number one Victoria Azarenka to also reach the semi-finals.

The 23-year-old Halep, of Romania, chasing her first grand slam singles title, came out strong against the Belarussian after an 85-minute, third-set rain delay to secure a 6-3 4-6 6-4 victory and a last-four clash against Pennetta.

"It was a tough match. I'm really happy that I could win, I don't know where it comes, the power to win this match," said the diminutive, but hard-hitting Halep.

Halep was run ragged in the second set by Azarenka who sent her scurrying from corner to corner as she fought back to level the quarter-final at one set apiece.

A light rain forced them off the court in the fourth game of the third set but when they returned to Arthur Ashe Stadium, a revived Halep took command.

Top seed Serena Williams, bidding to complete the fourth women's calendar-year Grand Slam sweep, faces Roberta Vinci of Italy in Thursday's other scheduled semi-final.

Source: Reuters